It is a long trip to the outer reaches of the Solar System. Planetary scientists who are eager to explore Jupiter and the planets beyond tend to plan their experiments not in terms of years, but generations. And so it is with some rejoicing, and also relief, that they have another mission on the books.

Last week, the European Space Agency (ESA) announced that it had selected the Jupiter Icy moons Explorer, or JUICE, a solar-powered behemoth that, at 4.8 tonnes, would be the heaviest interplanetary probe ever flown by Europe. It would launch in 2022 and arrive at Jupiter almost eight years later. After a few flybys of Jupiter's moons Callisto and Europa, in 2032 the probe would settle into orbit around its primary target, the moon Ganymede, for at least a year of science. Ganymede's main mystery is its enigmatic magnetic field, the only moon in the Solar System to have one. But, like Europa, Ganymede also has a subsurface ocean — although one that is less enticing to astrobiologists because it is likely to be isolated, sandwiched between thick layers of ice that prevent interesting chemical interactions with the surface and the deep rocky mantle.

Still, JUICE came top in a competition that sent two other prospective European missions packing. One was an X-ray telescope that would have imaged objects such as black holes with greater precision and sensitivity than ever before. Another was a set of satellites that, flying in formation, would have sensed tiny ripples in the fabric of space caused by violent events such as black-hole mergers — thereby opening up a whole new field: observational gravitational-wave astronomy.

Neither mission was a dud scientifically; quite the opposite. The gravitational-wave mission, in particular, is viewed as representing a scientific revolution in the making. These missions failed in the competition because they were expensive, and were likely to bust ESA's budget of €1 billion (US$1.3 billion). And the reason ESA could not afford them was because both were originally designed as joint missions with the United States. When NASA pulled out, each mission tried to reduce its scope and lower its price tag, but that proved too difficult.

JUICE was also once married to a NASA mission, but in a more modern arrangement. The ESA mission would have had its own satellite and rocket launcher, as would NASA, which would have sent an orbiter devoted to studying Europa. When the budgetary rug was pulled out from under NASA's Europa orbiter, JUICE was in much better shape, politically and financially.

The lessons here would seem to be perverse: eschew tight collaborations and you will be rewarded for your independence. Avoid working with foreign agencies and you will be better off in the long run.

That might be true, but only from the perspective of a scientist interested in Ganymede — and only Ganymede. Without NASA involvement, plenty of Europan science has been lost. And had the two missions launched as a loose partnership, there would have been several ways in which the sum of the two missions was greater than its parts. For example, tracking the magnetosphere of the Jovian system using two probes makes a far better map than using just one.

The bigger point, however, is that the frontiers of science in many fields are reaching the stage — or price tag — at which no single country can go it alone. Just ask scientists who worked on completing the Human Genome Project, or building the Large Hadron Collider near Geneva, Switzerland. Of late, space scientists at NASA and ESA have no such project to hold up as an example. In addition to the X-ray and gravitational-wave observatories, other transatlantic partnerships have evaporated, including ones to study dark energy and to return samples from Mars. If a mission to the king of the planets is a cause for rejoicing, then the fact that it is so singular may be a cause for alarm.